A Risk Management Toolbox for Minimizing Induced Seismicity and Maximizing Production – HEU URGENT Update

Traditionally, in faulted/sedimentary systems, geothermal injection wells are drilled away from known faults to reduce the risk of induced seismicity, e.g., in the VITO geothermal project in Mol, Belgium. Unless there is high layer/matrix permeability in the area, this can limit the well capacity and result in prohibitively high injection pressures that can induce high stress changes on smaller potentially unknown faults in the area. Further, in geothermal applications, temperature changes in the subsurface may induce large stress changes that can also result in fault reactivation. As part of the HEU-URGENT project, a risk management toolbox has been developed to allow for more effective placement of geothermal wells in doublet systems to maximize heat production while minimizing the risk of induced seismicity.

An essential part of the risk management toolbox is the geomechanical solution to evaluate effective stress changes on known faults and structures in or near the reservoir. In this work, we evaluate three techniques for stress calculation. The first is a simple, but fast, 1D semi-analytical calculation based on Hooke’s law for elasticity. This approach allows for direct pore pressure and thermal stress effects to be considered but ignores elastic stress transfer and Poisson effects. The second semi-analytical approach utilizes the nucleus of strain concept to account for the elastic stress transfer and Poisson effects but comes at a higher computational cost. The third approach is a numerical finite element approximation of linear elastic material behavior. The pros and cons of each approach will be discussed, and the comparison of the results will be presented.